[v4,1/3] Documentation: Add documentation for new platform_profile sysfs attribute

Commit Message

Mark Pearson Nov. 26, 2020, 4:51 p.m. UTC

On modern systems the platform performance, temperature, fan and other
hardware related characteristics are often dynamically configurable. The
profile is often automatically adjusted to the load by some
automatic-mechanism (which may very well live outside the kernel).

These auto platform-adjustment mechanisms often can be configured with
one of several 'platform-profiles', with either a bias towards low-power
consumption or towards performance (and higher power consumption and
thermals).

Introduce a new platform_profile sysfs API which offers a generic API for
selecting the performance-profile of these automatic-mechanisms.

Co-developed-by: Mark Pearson <[e-mail]>
Signed-off-by: Mark Pearson <[e-mail]>
Signed-off-by: Hans de Goede <[e-mail]>
---
Changes in v2:
 - updated to rst format
Changes in v3 & v4:
 - version bump along with rest of patch series

 .../ABI/testing/sysfs-platform_profile.rst    | 66 +++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-platform_profile.rst

Patch

diff --git a/Documentation/ABI/testing/sysfs-platform_profile.rst b/Documentation/ABI/testing/sysfs-platform_profile.rst
new file mode 100644
index 000000000000..5f7b2a94409b
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-platform_profile.rst
@@ -0,0 +1,66 @@ 
+=======================================================================
+ Platform Profile Selection (e.g. /sys/firmware/acpi/platform_profile)
+=======================================================================
+
+
+On modern systems the platform performance, temperature, fan and other
+hardware related characteristics are often dynamically configurable. The
+profile is often automatically adjusted to the load by some
+automatic mechanism (which may very well live outside the kernel).
+
+These auto platform adjustment mechanisms often can be configured with
+one of several platform profiles, with either a bias towards low power
+operation or towards performance.
+
+The purpose of the platform_profile attribute is to offer a generic sysfs
+API for selecting the platform profile of these automatic mechanisms.
+
+Note that this API is only for selecting the platform profile, it is
+NOT a goal of this API to allow monitoring the resulting performance
+characteristics. Monitoring performance is best done with device/vendor
+specific tools such as e.g. turbostat.
+
+Specifically when selecting a high performance profile the actual achieved
+performance may be limited by various factors such as: the heat generated
+by other components, room temperature, free air flow at the bottom of a
+laptop, etc. It is explicitly NOT a goal of this API to let userspace know
+about any sub-optimal conditions which are impeding reaching the requested
+performance level.
+
+Since numbers on their own cannot represent the multiple variables that a
+profile will adjust (power consumption, heat generation, etc) this API
+uses strings to describe the various profiles. To make sure that userspace
+gets a consistent experience this API document defines a fixed set of
+profile names. Drivers *must* map their internal profile representation
+onto this fixed set.
+
+
+If there is no good match when mapping then a new profile name may be
+added. Drivers which wish to introduce new profile names must:
+
+ 1. Explain why the existing profile names canot be used.
+ 2. Add the new profile name, along with a clear description of the
+    expected behaviour, to the documentation.
+
+:What:        /sys/firmware/acpi/platform_profile_choices
+:Date:        October 2020
+:Contact:     Hans de Goede <[e-mail]>
+:Description: This file contains a space-separated list of profiles supported for this device.
+
+              Drivers must use the following standard profile-names::
+
+         		 low-power:     Low power consumption
+         		 cool:          Cooler operation
+		         quiet:         Quieter operation
+		         balanced:      Balance between low power consumption and performance
+		         performance:   High performance operation
+
+              Userspace may expect drivers to offer more than one of these
+              standard profile names.
+
+:What:        /sys/firmware/acpi/platform_profile
+:Date:        October 2020
+:Contact:     Hans de Goede <[e-mail]>
+:Description: Reading this file gives the current selected profile for this
+              device. Writing this file with one of the strings from
+              available_profiles changes the profile to the new value.